晶粒双峰分布与多尺度第二相复合强韧化镁合金的协同机制及可控制备

The national significant strategy demands in the field of aerospace, rail transit, etc. are in the urgent need of lightweight magnesium alloy. In order to overcome the bottleneck problems of low strength and poor ductility at room temperature for magnesium alloy, a collaborative strategy of the bimodal-grains and multiscale second-phase particles is proposed. The corresponding preparation technology and the principle of low temperature ECAP-Rolling-Short Time Annealing are being developed. By the integrated analysis of preparation-microstructure-property, the magnesium alloy plate, strip and sheet are expected to possess a high strength and ductility by using the proposed preparation technology. First, the formation mechanism of the bimodal-grains and multiscale second-phase particles will be revealed by careful investigating the elements segregation on the defect under the coupling effect of strain and heat, the dynamic precipitation mechanism of second-phase particles and the effect of second-phase particles on the recrystallization. An effective control technique of microstructure will be developed. Second, the strengthening and toughening mechanism of the bimodal-grains and multiscale second-phase particles will be ascertained by investigating the compatible deformation of the bimodal-grains and multiscale second-phase particles, and the effect of ultra-fine grain/fine grain size and second-phase particles pattern on the corresponding mechanical behavior. Finally, by means of the integrated analysis of preparation-microstructure-property, the magnesium alloy with optimal combination of strength and ductility will be obtained. The research contents in the proposal can provide a new strategy and technological approach for strengthening-toughening of magnesium alloys.

本项目瞄准航空航天、轨道交通等国家重大战略领域对轻量化镁合金的急需，针对限制镁合金发展与应用的强度低、室温塑性差的瓶颈问题，提出晶粒双峰分布和多尺度第二相协同复合强韧化的策略；发展逐级降温ECAP-轧制-短时退火工艺和原理，通过制备-结构-性能一体化分析，获得兼具高强度高塑性的高性能镁合金板材、带材和薄带。首先，研究合金元素在应变-热耦合作用下在缺陷处的偏析规律、第二相的动态析出机理及第二相对合金再结晶的影响规律，揭示超细晶/粗晶组合的晶粒双峰分布和多尺度第二相的形成机理，发展行之有效的组织调控技术；其次，研究超晶粒双峰分布与多尺度第二相的协调变形机制，分析超细晶/粗晶尺寸分布、第二相形态对合金力学性能的影响规律，揭示晶粒双峰分布和多尺度第二相协同复合强韧化机理。最后，通过制备-结构-性能一体化分析，利用微观组织调控实现镁合金强度和韧性的最佳匹配，为镁合金强韧化设计和制备提供新思路和技术。

异质组织结构设计是突破镁合金强度低、室温塑性差等瓶颈的新策略。本研究主要以AZ91等商用镁合金为对象，发展了等通道转角挤压（ECAP）组合热处理工艺，制备出了系列以组织异构为特征的镁合金。通过对合金基体、第二相及织构的多重调控，同步提升了合金的强度与塑性，为镁合金的高性能化提供了新思路和技术，并揭示了相关特征力学行为的微观起源，提出了基于组合ECAP工艺的异构组织的形成机制。进一步拓展了高强韧镁合金的同步耐蚀化研究，为高强韧镁合金的综合使役性能的提升提供了理论参考。. 重要研究发现：（1）由于部分再结晶，中温低道次ECAP组合高温短时时效加工AZ91镁合金具有多峰晶粒结构特征（粗细混晶+不均匀析出相）。晶粒细化、HDI强化和析出强化的协同作用提高了合金的强度，而晶粒细化和多峰晶粒结构所产生的额外的应变硬化改善了合金的塑性；（2）高温低道次ECAP组合时效加工产生了晶粒异构+析出异构的多级异构组织，合金获得了最佳的强塑性匹配，并表现出异于铸态合金的拉压不对称行为；（3）工业级ECAP组合部分预固溶及后时效加工实现了大体量多级异构AZ91镁合金块材的制备；（4）基面滑移协同柱面滑移的开动在高温多道次ECAP加工合金中形成了双织构组织，使合金强度各向异性显著，而拉伸塑性呈现准各向同性。. 本项目为期四年，执行期间已取得丰富的创新性成果，现已授权国家发明专利6项，在国内外行业核心期刊发表论文33篇。